Field of the Invention
The invention lies in the telecommunications field. More specifically, the invention pertains to a method and a device for generating a transmission signal, which comprises a number of antenna data signals provided for emission via in each case one transmitting antenna, and wherein the useful data signal is subjected to channel coding. The device generates from a useful data signal a transmit signal for emission via a plurality of antenna data signals each for emission via a respective transmitting antenna.
In mobile radio systems, the quality of transmission is influenced by time variance and frequency selectivity of the mobile radio channel and by time-variable multiple access interference. As a rule, digital mobile radio systems use several types of diversity for improving the system behavior. Known measures for utilizing the frequency diversity of the mobile radio channel are the use of a CDMA or TDMA component in multiple access. The time diversity of the channel is usually utilized by channel decoding and interleaving the data signal to be transmitted. A further type of diversity is space diversity. In space diversity, a distinction is made between antenna diversity, directional diversity and polarization diversity.
In the text which follows, antenna diversity is considered. Antenna diversity can be used because the state of the mobile radio channel differs for different sites of the mobile stations and base stations. In antenna diversity, a distinction is made between the case where a number of receiving antennas are used (receiver antenna diversity) and the case where a number of transmitting antennas are used (transmitter antenna diversity) and both possibilities can also occur combination. Whereas receiver antenna diversity is well understood from the theoretical point of view and is widely used in practice, the concept of transmitter antenna diversity has hitherto been researched less well.
Special turbo codes designed for transmitter antenna diversity have already been proposed. In these codes, the number of transmit data streams for the transmitting antennas are already generated during the coding. This procedure can be called antenna diversity coding.
The disadvantageous factor in this concept is that the number of transmitting antennas needed depends on the code rate Rc=k/n. The code rate Rc is the quotient of a number k of input data symbols and a number n of output data symbols (referred to the k input data symbols) of the coder. In the case of a code rate of, say, Rc=½, two transmitting antennas must be used whereas a code rate of Rc=⅓ requires a number of three transmitting antennas. If a variable service-dependent code rate is possible and provided, as in the UMTS (Universal Mobile Telecommunications System) standard, the method of antenna diversity coding is not feasible because every service (e.g. voice, video) needs a different number of transmitting antennas.
In the article “Fading Correlation and its Effect on the Capacity of Space-Time Turbo-Coded DS/CDMA Systems” by D. J. Wyk et al., Milcom 1999, IEEE Military Communications Conference Proceedings, Atlantic City, N.J., Oct. 31-Nov. 3, 1999, IEEE Military Communications Conference, New York, N.Y.: IEEE, US, Vol. 1 of 2 CONF. 18, Oct. 31, 1999, pages 538-42, a method and a device for antenna diversity coding for M transmitting antennas are described. A turbo coder performs coding with a code rate of 1/(M+1) and generates M+1 data streams. These are transformed by means of a puncturing device and multiplexer into M data streams which are subsequently emitted via the M transmitting antennas.
International publication Nr. WO 00/36783 describes a transmitting system comprising a number of two transmitting antennas. If the channel coder has a code rate of less than ½, data rate matching is performed by way of a puncturing unit.